With close monitoring and a few standard precautions,
nearly all children with known or
suspected vaccine allergies can be safely immunized,
according to a team of vaccine safety experts led
by the
Johns Hopkins Children's Center.

Writing in the September issue of Pediatrics,
the multicenter research team offers
pediatricians a step-by-step tool for quickly identifying
children with allergic reactions to vaccines,
and a much-needed guide, they say, to safely immunizing
those who are allergic.

Serious allergic reactions to vaccines are extremely
rare — one or two per million vaccinations,
according to some estimates — but when they happen,
such episodes can be serious, even life-
threatening, making it critical for pediatricians to
instantly spot true allergic reactions and
differentiate them from more benign nonallergic responses,
investigators say. It is also crucial that
pediatricians design a safe immunization plan for children
with confirmed vaccine allergies. Children
who have had one allergic reaction are believed to be at a
higher risk for future reactions, typically
more serious than the first.

"We cannot reiterate enough that the vaccines used
today are extremely safe, but in a handful
of children, certain vaccine ingredients can trigger
serious allergic reactions," said Robert Wood, lead
author on the paper and chief of Pediatric Allergy and
Immunology at the Johns Hopkins Children's
Center. "For the most part, even children with known
allergies can be safely vaccinated."

Given recent outbreaks of vaccine-preventable
infections such as measles, mumps and whooping
cough in the United States, and measles and polio overseas,
it is essential to safely vaccinate as many
children as possible, investigators say.

Combing through available evidence on vaccine safety
and allergies, the Johns Hopkins-led team
developed a sequence of instructions — an algorithm
— that prompts physicians one step at a time on how
to evaluate and immunize children with known or suspected
vaccine allergies.

The guidelines are intended for doctors and parents
who are uncertain about vaccine safety in
children who have already had or are at high risk for
having allergic reactions to vaccines.

In such cases, the Johns Hopkins–led group advises a
workup by an allergist, including skin prick
testing — a prick on the skin or an injection under
it with a small dose of vaccine or suspected allergen
from the vaccine — or blood tests that would detect
the presence of characteristic antibodies that
patients develop to allergens, such as antibodies to
gelatin or egg proteins used in several common
vaccines.

In many cases, allergic children can be vaccinated
using alternative forms of a vaccine that are
free of the allergen. Even if allergen-free formulations
are unavailable, many children can still be
vaccinated and remain under physician supervision for
several hours after vaccination. Another option
is testing the child to check for immunity. If blood tests
show the child has already developed
protective antibodies, it may be OK, at least temporarily,
to withhold further doses of the vaccine,
researchers write.

"Vaccines save lives, and parents should know that
children who have had allergic reactions
after a vaccine are likely to have developed protection
against infection as a result of the
vaccination," said investigator Neal Halsey, an infectious
disease specialist at the Johns Hopkins
Children's Center and professor of international health at
the Johns Hopkins Bloomberg School of
Public Health.

"Most children who have had an allergic reaction after
a vaccine can still be vaccinated against
other diseases safely, and some can receive additional
doses of vaccines they might have reacted to,"
Halsey said.

Many children with known vaccine allergies who have
low levels of protective antibodies and
require more doses can be vaccinated safely under the
guidelines. In some cases, children with known
allergies can be given anti-allergy medications, such as
antihistamines and corticosteroids, before
vaccination to help ward off or lessen the allergic
reaction.

Immunizations of children with known vaccine allergies
should always be administered under
medical supervision in a clinic equipped to treat
life-threatening allergic reactions or in a hospital
intensive-care unit. Patients can usually go home after an
hour or two if they have no adverse
reactions.

True allergies typically cause immediate reactions,
involving the immune system as a whole, that
occur within a few minutes to a few hours of vaccination.
By contrast, delayed reactions, which occur
within days, even weeks after vaccination, are generally
benign and are rarely, if ever, dangerous.

Symptoms of immediate allergic reactions include
hives, swelling, wheezing, coughing, low blood
pressure, vomiting and diarrhea, and can lead to full-blown
anaphylaxis, a life-threatening allergic
reaction.

The research was funded by the Centers for Disease
Control and Prevention.

Co-investigators on the research are Melvin Berger,
University Hospitals of Cleveland; Stephen
Dreskin, University of Colorado; Rosanna Setse, Johns
Hopkins University Bloomberg School of Public
Health; Renata Engler, Walter Reed Army Medical Institute;
and Cornelia Dekker, Stanford University
School of Medicine. The Clinical Immunization Safety
Assessment Network, consisting of six medical
research centers with expertise in immunization safety, was
part of the study.

Conflict of interest disclosure for Johns Hopkins
investigators: Halsey has received research
support from vaccine manufacturer Wyeth and is a consultant
for vaccine manufacturers
GlaxoSmithKline and Merck.